4 Sets
12 reps light weight
10 reps
10 heavier reps if possible
8 reps
8 heavy reps (as heavy as possible but doable)

Note: Start out light, probably empty barbell. If possible, increase weight each set to a heavy set of 8. Rest 90 seconds between sets. Brace your core and tighten up your abs when pushing up to avoid excessive arching of your back.